678 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



THE METHODS BY WHICH INFECTIOUS AGENTS ARE ELIMINATED FROM 



THE BODY 



The etiological microorganisms of the various infectious diseases 

 may be eliminated from the body in two general ways, namely, by a 

 direct method and by an indirect method. For a microorganism to 

 be directly eliminated from the body it is necessary for the focus of the 

 infection to communicate with the outside of the body in some way or 

 other. In the case of infections of the mucous membranes and the skin 

 there is, of course, direct communication with the outside. In diseases 

 of the respiratory organs and the intestines the infectious agents are 

 discharged into the lumen of the air passages and the intestines and then 

 thrown out from these passages. Examples of the partial direct elimi- 

 nation from the skin may be found in such diseases as smallpox, measles, 

 syphilis, scarlet fever, lupus vulgaris, and in suppurative conditions 

 such as carbuncles and furuncles. From the present evidence little 

 significance perhaps is to be attached to the elimination of the infectious 

 agents mentioned directly from the skin. It is probable that the micro- 

 organisms which are eliminated remain alive for only a short time and are 

 not factors of consequence in the transmission of these infections. As 

 examples of diseases in which direct elimination from the various 

 mucous membranes occurs, infections such as typhoid fever, tubercu- 

 losis, cholera and dysentery from the membranes of the intestines; 

 influenza, pneumonia and tuberculosis from the bronchial membranes; 

 diphtheria, leprosy, glanders and scarlet fever from the membranes of 

 the nose, throat, and tonsils; and gonorrhea, syphilis and tuberculosis 

 from the membranes of the genito-urinary tract may be mentioned. 

 In elimination from the various internal membranes sometimes re- 

 infections occur such as in the case of the elimination of Bact. tubercu- 

 losis from the respiratory tract, the swallowing of the sputum, and the 

 subsequent infection of the intestines. 



In the second, or indirect method of elimination, two distinct prop- 

 ositions present themselves; first, the infectious microorganism must 

 enter the lymphatic or blood circulation; and, secondly, in order to get 

 out of the body they must pass through the cells of some of the organs, 

 the mucous membranes or skin. It is a common occurrence for bac- 

 teria and other microorganisms to get into the circulation in some of 

 the infectious diseases such as typhoid fever, pneumonia, plague, 



